Composite materials are replacing traditional materials in aerospace and other industries because of their high strength to weight ratio, thermal characteristics, and other properties that can often be engineered for superior performance. For example, Organic and Ceramic Matrix Composites (CMCs) are being developed for high-temperature aerospace applications because of their light weight, high strength, superior wear resistance and dimensional stability at high temperatures. Components using these materials are being investigated for several engines.
Composite materials are not without their flaws and testing and validation is needed for quality control at production and for life management once deployed. Continuing the above example, CMCs that are most useful in aerospace structural applications have continuous fiber reinforcements embedded in a ceramic matrix. As such, these CMCs have mostly fiber-dominated mechanical properties and rely on the matrix materials for load transfer, increased strain and toughness, and, to some extent, environmental protection. However, at the elevated temperature environments typically found in advanced propulsion systems, these materials can react with the oxygen, moisture, and salt in the air to undergo chemical changes that can affect the structural performance and remaining life of components made from these materials, while showing no visible structural changes.
Nondestructive evaluation (NDE) techniques are needed that can provide relevant information about the material condition of the composite and constituents. These techniques also need to provide information about the influence of any degradation or changes in these constituents on the ultimate performance of a composite materials. This information can be used to both improve operational performance and reduce costs by improving repair/replace decisions. Also, there is a need for enhanced NDE and stress monitoring for carbon fiber composites including the need to rapidly image manufacturing quality for wide areas curved surfaces, to detect and characterize impact and fatigue/overload damage, to monitor stress and detect cracks in metal structural elements behind composite layers.